After becoming "obsessed" with a Bird and the Bee song, Grohl met Kurstin while vacationing in Hawaii. The two became friends and eventually Kurstin agreed to work onConcrete & Gold.

"We start recording, and our riffs go from heavy to huge," Grohl said. "It's clear that these songs that we have are going from Foo Fighters songs to something bigger than we'd ever done before in our entire lives.

The band recorded at EastWest studios in Hollywood, California.

Grohl said that beyond the history of the studios and the great sounding rooms, the Foo Fighters benefitted from the studio's constant stream of pop stars.

"One weekLady Gaga's there. Another week,Jason Bonhamis there. The place is legendary; it's unbelievable," Grohl says of his many celebrity encounters.

But the Foo Fighters are one of the biggest rock bands around, so when Grohl started asking artists if they'd like to sing, not many of them turned him down.

"At this point, all bets are off, let's just get everybody to come in and play," he says.